Method of operating an anti-lock automotive vehicle brake system

ABSTRACT

The present invention discloses a method of operating an anti-lock automotive vehicle brake system for driving stability control and/or traction slip control (DSC/TCS) including a brake power booster operable irrespective of the driver&#39;s wish. According to this method, the brake power booster is actuated irrespective of the driver&#39;s wish for prefilling the vehicle wheel brakes, and further pressure increase in the vehicle wheel brakes upon completion of the prefilling action is carried out by the ABS return pump.

BACKGROUND OF THE INVENTION

The present invention relates to a method of operating an anti-lockautomotive vehicle brake system for driving stability control and/ortraction slip control, including a pneumatic brake power boosteroperable irrespective of the driver's wish and a master brake cylinderconnected downstream of the brake power booster, the pressure chambersof the master brake cylinder being connected to wheel brakes associatedwith the individual vehicle wheels by way of an ABS hydraulic unithaving a return pump.

German patent No. 42 08 496 discloses a brake system, wherein the brakepower booster interacts with a solenoid valve to achieve automaticallycontrolled braking operations along with a great deceleration of thevehicle. The solenoid valve permits an enhanced use of the brakingpressure upon quick application of the brake pedal. A brake pedalposition sensor, a brake light switch and a force sensor permittingdetection of the driver's wish for deceleration are provided to achievethe above-mentioned braking pressure control concept. Further, the knownbrake system includes an anti-lock control system (ABS) which ensures astable deceleration behavior of the vehicle during braking operations.

However, the patent referred to hereinabove does not provide anyspecific indications as to how the described brake system could be usedfor driving stability control.

German patent application No. 42 32 311 discloses a hydraulic vehiclebrake system with an anti-lock control device having anauxiliary-pressure source for the improvement of the vehicle directionalstability, in particular when cornering, by automatic braking. Theauxiliary-pressure source is used to prefill the vehicle wheel brakesand to precharge the return pump. The auxiliary-pressure source, whichis provided by parallel connection of an auxiliary pump, a throttle andan auxiliary-pressure limiting valve, is connected to an inlet port ofone hydraulic cylinder each. The hydraulic cylinder is connected to theconnection between the outlet of an actuating unit, comprised of a brakepower booster and a master cylinder inserted downstream of the mastercylinder, and the ABS hydraulic unit or the wheel brake. A second inletof the cylinder is connected to the master brake cylinder, and aseparating piston which can be acted upon by auxiliary pressure isguided in the cylinder. The separating piston accommodates a valve whichis open in its inactive position and permits a connection between themaster brake cylinder and the wheel brake. When the auxiliary pump isstarted, the separating piston is displaced, with the result that thevalve closes the above-mentioned connection and the pressure fluidvolume conducted by the separating piston causes prefilling of the wheelbrakes and precharging of the return pump.

A disadvantage of this brake system is, however, the comparativelyextensive technical effort and structure required to achieve the knownmethod.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to disclose a method ofoperating an anti-lock automotive vehicle brake system of the previouslymentioned type which permits being achieved in a simple and low-costmanner by use of component parts which are already provided in the brakesystem.

A first objective achieved by the present invention involves theactuation of the brake power booster irrespective of the driver's wishupon commencement of the control to prefill the wheel brakes, and thefurther pressure increase in the wheel brakes is carried out by way ofthe return pump after completion of the prefilling action.

To measure the hydraulic pressure, introduced by the driver, by way oflow-cost pressure sensors, it is favorable that after prefilling of thewheel brakes, the actuation of the brake power booster irrespective ofthe driver's wish (independent actuation) is deactivated.

In another aspect of the present invention, a favorable supply of thereturn pump with pressure fluid is achieved because the actuation of thebrake power booster irrespective of the driver's wish (independentactuation) is maintained after the prefilling of the wheel brakes. It isadvantageous, especially at low temperatures, that aspiration of thepressure fluid from the pressure fluid supply reservoir by way of opencentral valves, provided in the master brake cylinder, is not required.

In still another aspect of the present invention, the load on the returnpump, which is caused during control operations due to the simultaneousactuation by the driver and the independent actuation of the brake powerbooster, is limited because the actuation of the brake power booster bythe driver is sensed and the actuation irrespective of the driver's wish(independent actuation) is reduced accordingly.

To identify the hydraulic pressure introduced by the driver and/or thebrake power booster, the hydraulic pressure introduced into the masterbrake cylinder is continuously determined according to the presentinvention. To achieve a redundant information about pressure values, thepressure is determined by pressure sensors connected to the pressurechambers of the master brake cylinder according to the presentinvention. The driver's wish for deceleration may be determined by thesevalues, when the maximum output of the brake power booster is as known.

In a preferred aspect of the present invention, a reliableidentification of the driver's wish for deceleration is ensured bysensing the actuating force which is introduced at a pedal actuating thebrake power booster.

In another favorable aspect of the present invention, the outputpressure of the return pump is limited, preferably to a valuerecommended for intervention by a car maker.

In still another favorable aspect of the present invention, adequatepressure fluid supply of the return pump is ensured in that the suctionside of the return pump can be acted upon by the master brake cylinderpressure.

Further, it is required for the operation that the hydraulic connectionbetween the master brake cylinder and the suction side of the returnpump can be opened or closed at any master brake cylinder pressuresdesired. Preferably, the hydraulic connection is closed only until thepressure fluid volume, which is stored in a low-pressure accumulatorconnected to the suction side of the return pump, has been conducted tothe pressure side of the return pump. It is ensured by this arrangementthat the pressure fluid supply of the return pump is not interruptedwhen the low-pressure accumulator is evacuated.

The second objective achieved by the present invention involves using avolume of pressure fluid, which is stored in a pressure accumulator, forprefilling the wheel brakes upon the commencement of the control.

The dynamics of the above-mentioned pressure control is increased inparticular in that the pressure accumulator is connected to the pressureside of the return pump by way of a shut-off valve when the deliveryrate of the return pump is not sufficient to perform pressure controloperations.

In still another aspect of the present invention, the pressureaccumulator is charged when the delivery rate of the return pump issufficient to simultaneously charge the pressure accumulator and performthe desired pressure control operation, or in the absence of a pressureincrease period in any one of the connected wheel brakes. In thisarrangement, the charging condition of the pressure accumulator may bemonitored by a pressure sensor or a position sensor which determines theposition of the pressure accumulator piston, for example.

The present invention will be explained in the following by way of twoembodiments, making reference to the accompanying drawings.

BRIEF SUMMARY OF THE DRAWINGS

In the drawings,

FIG. 1 is a first embodiment of an anti-lock automotive vehicle brakesystem by which the first solution of the method of the presentinvention may be realized.

FIG. 2 is a second embodiment of an anti-lock automotive vehicle brakesystem by which the second solution of the method of the presentinvention may be realized.

DETAILED DESCRIPTION OF THE INVENTION

The brake system of the present invention to implement the method of theinvention, as shown, includes two brake circuits I and II having acompletely identical design. Thus, the following description of onebrake circuit also applies to the other brake circuit. The brake systemshown generally includes two braking pressure generators 1, 2 which areoperable independently of each other and to which wheel brake cylinders17, 18 are connectable by way of hydraulic lines (not referred to).Further, the brake system includes an electronic control unit withassociated sensor means (not shown) The wheel brake cylinders 17, 18 ofthe individual brake circuits I, II are associated such that the firstwheel brake cylinder 17 either is associated with a wheel of one vehicleaxle and the other wheel brake cylinder 18 is associated with thediagonally opposite wheel of the other vehicle axle (diagonal split-upof the brake circuits), or both wheel brake cylinders 17 and 18 areassociated with the same vehicle axle (black and white split-up of thebrake circuits).

The first pressure generator 1 operable by the driver of the automotivevehicle by way of a brake pedal 6 includes a brake power booster 5,which may be a pneumatic booster, for example. A master brake cylinder,preferably a tandem master cylinder 3, is connected downstream of thebrake power booster. The pressure chambers (not shown) of the tandemmaster cylinder are connectable to a pressure fluid supply reservoir 4.An actuating rod 27 is coupled to the brake pedal 6 permitting actuationof a control valve 8 (shown only schematically) which controls theincrease of a pneumatic differential pressure in the housing of thevacuum brake power booster 5. A solenoid (not shown), operable bycontrol signals of the electronic control unit, permits an independentactuation of the control valve 8 irrespective of an actuating forceintroduced at the brake pedal 6.

A brake light switch 14 which is operatively connected to the brakepedal 6 permits identifying the actuation of the brake power booster 5by the driver or by an independent actuation. The brake pedal 6 isentrained and the brake light switch 14 is thereby reversed duringindependent actuation of the brake power booster 5. Actuation of thebrake power booster 5 initiated by the driver can be detected by use ofa release switch (not shown).

The second pressure generator 2 is configured as a motor-and-pumpassembly which includes a hydraulic return pump 7 driven by an electricmotor (not shown). The suction side of the return pump is connected tothe first pressure chamber of the master brake cylinder 3 by a firstnon-return valve 24 and an electromagnetically operable switching valve9. The pressure fluid flows from the pressure side of the return pump 7to a hydraulic junction 21 by way of a second non-return valve 25 and adamping chamber (not shown). A line portion 38 leading to the firstwheel brake cylinder 17 and a line portion 39 leading to the secondwheel brake cylinder 18 are connected to junction 21. A hydraulic line23 connects the pressure side of the return pump 7 to the tandem mastercylinder 3. Further, a preferably electromagnetically operableseparating valve 10 is interposed between the junction 21 and the masterbrake cylinder 3. A third non-return valve 31 and a pressure-limitingvalve 28 are connected in parallel to the separating valve 10. Aparallel connection of an inlet valve 11 with a fourth non-return valve29 and an outlet valve 12 is used for the modulation of the pressureintroduced into the first wheel brake cylinder 17. The mentionedparallel connection is provided in the line portion 38, and the outletvalve 12 permits a connection between the first wheel brake cylinder 17and a low-pressure accumulator 13 for the reduction of the wheel brakingpressure. The low-pressure accumulator 13 is connected to the suctionside of the return pump 7 by way of a fifth non-return valve 30.

A second parallel connection of a second inlet valve 15 with a sixthnon-return valve 40 and a second outlet valve 16 is provided to controlthe hydraulic pressure introduced into the second wheel brake cylinder18 associated with the brake circuit at topic, which is similar to thewheel brake cylinder 17 referred to hereinabove. The mentioned parallelconnection is arranged in the line portion 39, and the outlet valve 16provides a connection between the second wheel brake cylinder 18 and thelow-pressure accumulator 13 for the reduction of wheel braking pressure.

To identify pressure variations in the tandem master brake cylinder 3initiated by the driver, a means to determine the master brake cylinderpressures is provided in both brake circuits I, II which, preferably, isconfigured as pressure sensors 32, 33 connected to the first and thesecond brake circuits I, II.

During normal braking operations, pressure increase and pressurereduction in the wheel brake cylinders 17, 18 can be effected by acorresponding operation of the first braking pressure generator 1 by wayof the open separating valve 10 and the open inlet valves 11, 15.

The return pump 7 is started during ABS control operations in animminent locked condition of the wheel associated with the wheel brake17, for example. Both the switching valve 9 and the separating valve 10remain non-actuated. The pressure is modulated by correspondinglyswitching the inlet and outlet valves 11 and 12, and the pressure fluiddischarged into the low-pressure accumulator 13 is returned by thereturn pump 7 until the pressure level of the master brake cylinder isreached.

Upon commencement of each independently actuated braking operation, thebrake power booster 5 is actuated irrespective of the driver's wish,during the starting period of the return pump 7, so that the wheelbrakes 17, 18 are prefilled. The separating valve 10 is closed and theswitching valve 9 is opened for further pressure increase. The result isthat the return pump 7 generates a high pressure at the junction 21which is limited by the pressure-limiting valve 28 to permit individualadjustment of the desired independent braking pressure in the wheelbrake cylinders 17, 18 by switching the ABS inlet and outlet valves 11,13 and 12, 16. After switch-over of the valves 9 and 10, actuation ofthe brake power booster 5 may be reduced to such an extent that thesuction side of the return pump 7 is supplied with a still sufficientpressure fluid flow. The pressure prevailing in the master brakecylinder 3, which was adjusted due to simultaneous operation of thebrake power booster 5 by the driver and the independent actuation, ismonitored continuously by the pressure sensors 32, 33. It may also beexpedient to monitor the actuating force introduced by the driver by wayof a force sensor.

Pressure is increased by way of the open inlet valve 11. A period inwhich the pressure is maintained constant is achieved by switch-over ofthe inlet valve 11, while pressure is reduced by switch-over of theoutlet valve 12, when the inlet valve 11 is still closed. The pressurevariation required for the control is produced by pressure increaseperiods, pressure maintain-constant and pressure reduction periods. Thepressure fluid discharged into the low-pressure accumulator 13 isreturned by the return pump 7. This is done by the switching valve 9which adopts its closed condition by way of separation of the suctionside of the return pump 7 from the master brake cylinder 3 until thelow-pressure accumulator 13 is emptied.

The brake power booster 5 is configured as a known vacuum brake powerbooster, which is operable only by the brake pedal 6, in the brakesystem shown in the embodiment of FIG. 2. The design of the brake systemcorresponds mainly to the brake system previously described with respectto the embodiment of FIG. 1. In the embodiment of FIG. 2, a hydraulicpressure accumulator 20 is connected to the hydraulic junction 21 by theintermediary of a shut-off valve 19. The charging condition of thepressure accumulator 20 is monitored by a pressure or travel sensor 34.

The wheel brakes 17, 18 in the brake system shown in FIG. 2 areprefilled during the starting period of the return pump 7 by opening theshut-off valve 19, with the result that the pressure fluid volume storedin the pressure accumulator 20 becomes available. When the electroniccontrol unit (not shown) detects that the fluid flow through theshut-off valve 19 changes its direction to the effect of charging thepressure accumulator 20, the entire pump fluid volume is supplied forfurther pressure increase to the wheel brakes 17, 18 by closure of theshut-off valve 19.

As soon as the running return pump 7 has reached its nominal deliveryrate, or in the absence of need of pressure increase in any one of thewheel brakes 17, 18, the shut-off valve 19 may be re-opened to permitrecharge of the pressure accumulator 20.

We claim:
 1. A method of operating an anti-lock automotive vehicle brakesystem for driving stability control and/or traction slip control,including a pneumatic brake power booster operable irrespective of thedriver's wish and a master brake cylinder connected downstream of thebrake power booster, wherein the pressure chambers of the master brakecylinder are connected to wheel brakes associated with the individualvehicle wheels by way of an ABS hydraulic unit having a separating valvein each connection between the master brake cylinder and the wheelbrakes and a return, whereby, upon commencement of the driving stabilitycontrol and/or traction slip control, the brake power booster isactuated irrespective of the driver's wish for prefilling the wheelbrakes, characterized in that, after prefilling the wheel brakes, eachconnection between the master brake cylinder and the wheel brakes isclosed by means of the respective separating valve, and the furtherpressure increase in the wheel brakes is carried out by way of thereturn pump.
 2. The method as claimed in claim 1, characterized in that,after prefilling of the wheel brakes, the actuation of the brake powerbooster irrespective of the driver's wish is deactivated.
 3. The methodas claimed in claim 1, characterized in that, after prefilling of thewheel brakes, the actuation of the brake power booster irrespective ofthe driver's wish is maintained.
 4. The method as claimed in claim 1,characterized in that the actuation of the brake power booster by thedriver is sensed, and the actuation irrespective of the driver's wish isreduced accordingly.
 5. The method as claimed in claim 1, characterizedin that the hydraulic pressure introduced into the master brake cylinderis determined continuously.
 6. The method as claimed in claim 5,characterized in that the pressure is determined by pressure sensorsconnected to the pressure chambers of the master brake cylinder.
 7. Themethod as claimed claim 1, characterized in that the actuating forcewhich is introduced by a pedal actuating the brake power booster issensed.
 8. The method as claimed in claim 1, characterized in that theoutput pressure of the return pump is limited.
 9. The method as claimedin claim 3, characterized in that the suction side of the return pumpcan be acted upon by the master brake cylinder pressure.
 10. The methodas claimed in claim 9, characterized in that the hydraulic connectionbetween the master brake cylinder and the suction side of the returnpump is opened or closed at any master brake cylinder pressures desired.11. The method as claimed in claim 10, characterized in that thehydraulic connection between the master brake cylinder and the suctionside of the return pump is closed only until the pressure fluid volume,which is stored in a low-pressure accumulator connected to the suctionside of the return, has been conducted to the pressure side of thereturn pump.